Wednesday, October 19, 2005

Explosives alarm

Airports and border checks could improve security using a new type of explosives scanner patented by Lawrence Berkeley National Laboratory (LBNL) in California, on behalf of the US Department of Energy.

Existing security systems use X-ray wavelengths to look at the shape and density of suspect objects. The LBNL system could, however, pick up explosives automatically, by firing a beam of neutrons through a target bag or package.

The neutrons target the high levels of nitrogen found in most explosives, causing the material to emit gamma rays, which can then be detected using a simple sensor. As an added bonus, the neutron beam causes fissile materials to release more neutrons. So a combined gamma and neutron detector should be able to spot explosives or potential nuclear contraband in a single swoop.

A prototype neutron beam-based probe developed at the lab has a coil in the centre, surrounded by a layer of deuterium gas and a titanium shield. When a high-frequency radio signal is fed through the coil, the gas emits ions that bombard the titanium to release neutrons.

Output from the probe is a thousand times more powerful than other designs, the patent says, but a shaped shielding steers the neutrons forwards and away from the operator, making the system safe to use. The same approach could perhaps also be used to locate buried landmines, the creators suggest.